ABSTRACT
The means to gain access to the product from a biological source is the primary consideration during downstream processing of proteins. Traditionally, the choice of a protein source was restricted to the natural biological material producing it in sufficient amounts. But recombinant DNA technology has completely changed the scenario by allowing protein production in a biological host of choice. Microorganisms clearly constitute the most common production systems for industrial enzymes and other proteins. Mammalian cell hosts are preferred only when correct posttranslational modification is essential for the function of eukaryotic proteins. Insect cells are also emerging as production systems; however, the posttranslational processing differs from the mammalian cell systems.
